They don't have sheer numbers unless they go full mobilization. They already put almost entire Russian ground force, which is 280k, into battle almost 200k of it went into Ukraine with initial invasion force. And since then they've been moving everything they have left into Ukraine(military contingent from karabakh and abkhazia regions, troops from far east etc.). 1 million is the capacity of their whole military, and ground troops that could be used in the invasion are only the fraction of it(airforce is useful, but can't be used as ground troops, fleet isn't that useful TBH and only fraction of it is in the Black sea right now and they can't get more there). And they need at least someone to guard their borders(and Russia's borders are vast).